1. Field of the Invention
The present invention relates to a moving image communication device and a moving image communication system connected to networks, such as the Internet and Intranet, directly or via a LAN cable so as to transmit moving image data to a client, and to a semiconductor integrated circuit used for the communication of the moving image data.
2. Description of the Related Art
In response to the advancement of moving image compression technology, a network camera system for delivering digital moving images via networks such as the Intranet and Internet has been developed, and an increasing number of such camera systems are being made commercially available. In the system of this type, a digital camera (provided with a moving image communication device) is connected to the network via the LAN or wireless LAN, and moving image data generated in the digital camera, which is addressed to a specific reproduction device, is transmitted to the network via the moving image communication device. Because a network whose reliability is low is used in the communication, data is packetized, and the arrival of the packet is monitored at the terminal of a communication path. If a packet is found not to have arrived yet, for example, the packet is re-transmitted. Thus, measures are taken in order to prevent the omission of any packet so as to guarantee that the data is identical before and after the transmission.
Moving image data is incessantly generated in real time in the moving image communication device, which makes it an indispensable issue to guarantee the real-time transmission. Otherwise, it becomes impossible to reproduce the moving image in the reproduction device. An effective way to guarantee the real-time transmission is to continue the transmission irrespective of any packet missing on the network, which, however, results in the failure to accurately reproduce the moving image data. As a result, the delivery of the moving image, which is the object of the network camera system, cannot be realized.
In order to solve the foregoing problem, a camera system of a network storage type, which is recited in the Unexamined Japanese Patent Publication No. 2003-18525, was proposed. In the system, packets are managed in a moving image data storage server provided on the network, and the moving image data storage server performs the communication with the moving image communication device so that any packet missing on the network is interpolated and stored. Accordingly, the packets are interpolated in a state where the network is established between the moving image communication device and the moving image data storage server (in a state where the communication is maintained). As a result, the real-time transmission can be realized without the loss of any packet.
The camera system of the network storage type, however, is still disadvantageous in that the data may be missing depending on the communication conditions. More specifically, the camera system of the network storage type fails to respond to the following cases:
1) the real-time transmission is not possible due to congestion in network bands; and
2) the network is physically shut down.